1. Field of the Invention
This invention relates to electrical systems comprising a PTC or NTC device.
2. Summary of the Prior Art
Conductive polymer compositions [including such compositions which exhibit positive temperature coefficient (PTC), zero temperature coefficient (ZTC) or negative temperature coefficient (NTC) behavior] and electrical devices comprising them, including circuit control devices containing PTC elements, are known. Reference may be made for example to U.S. Pat. Nos. 2,978,665 (Vernet et al), 3,243,753 (Kohler), 3,311,862 (Rees), 3,351,882 (Kohler et al), 4,017,715 (Whitney et al), 4,085,286 (Horsma et al), 4,095,044 (Horsma et al), 4,177,376 (Horsma et al) 4,177,446 (Diaz) 4,421,582 (Horsma et al), 4,238,812 (Van Konynenburg et al), 4,255,698 (Simon), 4,276,466 (Middleman et al), 4,272,471 (Walker) 4,445,026 (Walker), 4,304,987 (Van Konynenburg), 4,388,607 (Toy et al), 4,315,237 (Middleman et al), 4,329,726 (Middleman et al), 4,442,139 (Brigham), 4,429,216 (Brigham), 4,413,301 (Middleman et al), 4,314,231 (Walty), 4,352,083 (Middleman et al), 4,317,027 (Middleman et al) 4,314,230 (Cardinal et al) and 4,330,704 (Jensen), and to copending and commonly assigned applications Ser. Nos. 84,352 (Horsma et al), 141,988 (Fouts et al), 141,989 (Evans) and 141,999 (Fouts et al). The disclosure of each of these patents and patent applications is incorporated herein by reference.
Although they suffer from a number of disadvantages by comparison with circuit protection devices comprising conductive polymers, circuit protection devices comprising ceramic PTC materials, e.g. doped barium titanates, are also known. Reference may be made for example to the article entitled "The PTC Resistor" by R. F. Blaha in Proceedings of the Electronic Components Conference, 1971, the disclosure of which is incorporated by reference herein.